Display element, photosensitive composition and electrowetting display

ABSTRACT

The present invention relates to a display element, a photosensitive composition and an electrowetting display. The display element includes: a first electrode layer stack; a second electrode layer stack; a housing space formed between the first and second electrode layer stacks; and a partition wall compartmentalizing the housing space, wherein the housing space contains at least a polar liquid and a non-polar liquid that are immiscible with each other, a surface layer in contact with the partition wall exists on the surface of at least one of the first and second electrode layer stacks that is in contact with the housing space, and an absolute value of the difference in linear expansion coefficient between the partition wall and the surface layer is 150 ppm/K or less.

TECHNICAL FIELD

The present invention relates to a display element, a photosensitivecomposition and an electrowetting display.

BACKGROUND ART

An electrowetting phenomenon is a phenomenon which utilizes a change incontact angle of a hydrophobic surface against a polar liquid (and anon-polar liquid) that is induced by, for example, application of avoltage to the polar liquid and non-polar liquid (usually colored) thatare immiscible with each other on an electrode having the hydrophobicsurface.

Usually, this non-polar liquid is enclosed in a space compartmentalizedby a partition wall.

Elements utilizing this electrowetting phenomenon show high brightnessand high contrast ratio as well as large viewing angle, high switchingrate and the like, and display elements utilizing this phenomenon haverelatively low power consumption because they do not require front orbacklight. Therefore, such elements are used in a variety of opticalapplication fields, including optical switches for optical fibers,optical shutters or filters for cameras and guide devices, opticalpickup elements, optical waveguide materials, video display pixels andthe like.

For example, Patent Documents 1 and 2 disclose display elementsutilizing such a phenomenon.

PRIOR ART REFERENCES Patent Documents

-   [Patent Document 1] JP-T-2013-542465-   [Patent Document 2] JP-A-2013-92701

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The above-described display elements display letters, figures and thelike in response to a change in the state of a non-polar liquid based onthe presence or absence of an applied voltage; therefore, leakage of thenon-polar liquid, which is enclosed in a space compartmentalized by apartition wall, into other space tends to make the display elementsunable to perform proper display.

Accordingly, it is required that the space compartmentalized by thepartition wall be such a space that does not allow the non-polar liquidto leak out into other space.

Further, since the above-described display elements display letters,figures and the like in response to a change in the state of a non-polarliquid based on the presence or absence of an applied voltage, it isdesired that the change in the state of the liquid based on the presenceor absence of an applied voltage be performed smoothly. Along with thedemand for an increase in the service life of display elements, it isalso demanded that the change in the state of the liquid be performedstably over a prolonged period of time.

Conventional display elements, however, still have room for improvementto satisfy these demands.

The present invention was made in view of the above-described demands,and an object of the present invention is to provide a display elementcapable of smoothly and stably changing the state of a non-polar liquidcontained therein over a prolonged period of time based on the presenceor absence of an applied voltage, in which display element cracking ordetachment between a partition wall and a layer in contact therewith isnot likely to occur.

Technical Solution

Under such circumstances, in order to solve the above-describedproblems, the present inventors intensively studied and discovered thatthe above-described problems can be solved by a display elementcomprising: a first electrode layer stack; a second electrode layerstack; a housing space which contains a polar liquid and a non-polarliquid that are immiscible with each other and is formed between thefirst and second electrode layer stacks; and a partition wallcompartmentalizing the housing space, an absolute value of thedifference in thermal linear expansion coefficient between the partitionwall and a surface layer in contact with the partition wall being in aprescribed range, the surface layer existing on the surface of at leastone of the first and second electrode layer stacks that is in contactwith the housing space, thereby completing the present invention.

Examples of the constitution of the present invention are describedbelow.

[1] A display element, comprising: a first electrode layer stack; asecond electrode layer stack; a housing space formed between the firstand second electrode layer stacks; and a partition wallcompartmentalizing the housing space, wherein the housing spacecomprises at least a polar liquid and a non-polar liquid that areimmiscible with each other, a surface layer in contact with thepartition wall exists on the surface of at least one of the first andsecond electrode layer stacks that is in contact with the housing space,and an absolute value of the difference in thermal linear expansioncoefficient between the partition wall and the surface layer is 150ppm/K or less.

[2] The display element according to [1], wherein the partition wall hasa thermal linear expansion coefficient of 0.1 to 150 ppm/K.

[3] The display element according to [1] or [2], wherein the partitionwall is a film obtained from a photosensitive composition.

[4] The display element according to any one of [1] to [3], wherein thepartition wall is a film obtained from a negative photosensitivecomposition.

[5] The display element according to [4], wherein the negativephotosensitive composition comprises an alkali-soluble polymer, across-linking agent and a photoinitiator.

[6] The display element according to [5], wherein the cross-linkingagent is at least one compound selected from the group consisting ofethylenically unsaturated group-containing compounds, epoxy group oroxetanyl group-containing compounds and alkoxyalkyl group-containingcompounds.

[7] The display element according to [5] or [6], wherein thealkali-soluble polymer is a compound having at least one functionalgroup selected from the group consisting of a carboxyl group, a phenolichydroxyl group and a silanol group.

[8] The display element according to any one of [5] to [7], wherein thealkali-soluble polymer is at least one polymer selected from the groupconsisting of acrylic resins, polyimides, polybenzoxazoles,polysiloxanes, polyolefins, cardo skeleton-containing resins and novolacresins.

[9] The display element according to any one of [5] to [8], wherein thealkali-soluble polymer has a weight-average molecular weight of 1,000 to100,000.

[10] A photosensitive composition for forming a partition wall, saidpartition wall compartmentalizing a first electrode layer stack, asecond electrode layer stack and a housing space which is formed betweenthe first and second electrode layer stacks and comprises a polar liquidand a non-polar liquid that are immiscible with each other, wherein anabsolute value of the difference in thermal linear expansion coefficientbetween the partition wall and a surface layer is 150 ppm/K or less, thesurface layer existing on the surface of at least one of the first andsecond electrode layer stacks that is in contact with the housing spaceand being in contact with the partition wall.

[11] The photosensitive composition according to [10], which is anegative composition comprising an alkali-soluble polymer, across-linking agent and a photoinitiator.

[12] An electrowetting display, comprising the display element accordingto any one of [1] to [9].

[13] The electrowetting display according to [12], comprising a colorfilter layer.

Advantageous Effects of Invention

According to the present invention, a display element capable ofsmoothly and stably changing the state of a non-polar liquid containedtherein over a prolonged period of time based on the presence or absenceof an applied voltage, in which display element cracking or detachmentbetween a partition wall and a layer in contact therewith is not likelyto occur, can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view showing one example of thedisplay element of the present invention.

FIG. 2 is a schematic plan view showing a partition wall(lattice-patterned coating film) obtained in an Example.

MODE FOR CARRYING OUT THE INVENTION

<<Display Element>>

The display element according to the present invention is representedby, for example, FIG. 1, and comprises: a first electrode layer stack11; a second electrode layer stack 12; a housing space 16 which isformed between the first electrode layer stack 11 and the secondelectrode layer stack 12; and a partition wall 13 whichcompartmentalizes the housing space 16, wherein the housing space 16comprises at least a polar liquid 15 and a non-polar liquid 14 that areimmiscible with each other, a surface layer (not shown) in contact withthe partition wall exists on the surface of at least one of the firstelectrode layer stack 11 and the second electrode layer stack 12 that isin contact with the housing space, and an absolute value of thedifference in thermal linear expansion coefficient between the partitionwall 13 and the surface layer is 150 ppm/K or less.

The absolute value of the difference in thermal linear expansioncoefficient between the partition wall and the surface layer is 150ppm/K or less, preferably 130 ppm/K or less, more preferably 110 ppm/Kor less, particularly preferably 100 ppm/K or less. Specifically, theabsolute value of the difference in thermal linear expansion coefficientcan be measured by the method described in the section of Examplesbelow.

When the absolute value of the difference in thermal linear expansioncoefficient is in the above-described range, cracking and detachmentbetween the partition wall and the surface layer in contact therewith isnot likely to occur. Particularly, even if the display element is usedunder a high-temperature or low-temperature condition, such cracking anddetachment is not likely to occur. Thus, according to the presentinvention, a display element comprising such a housing space that doesnot allow a non-polar liquid to leak out into other space, which displayelement has excellent durability and display properties, can beobtained. Further, if the absolute value of the difference in thermallinear expansion coefficient is in the above-described range, a displayelement capable of smoothly and stably changing the state of a non-polarliquid contained therein over a prolonged period of time based on thepresence or absence of an applied voltage can be obtained.

In the present invention, there are cases where the partition wall andthe electrode layer stack(s) are adhered using an adhesive or the like.In such cases, the above-described surface layer is not an adhesivelayer and refers to a layer existing on the surface of the electrodelayer stack(s) that is in contact with the housing space.

In FIG. 1, there is the surface layer on the first electrode layer stack11 that is in contact with the housing space 16. The surface layer is ahydrophobic layer. Thus, in a display element 10, when no voltage isapplied (“turn off” in FIG. 1), the non-polar liquid (colored liquid) 14exists evenly such that it covers the surface of the first electrodelayer stack 11. Meanwhile, when voltage is applied to this displayelement 10 (“turn on” in FIG. 1), the non-polar liquid 14 exists in asubstantially hemispherical shape near the partition wall 13.

In this manner, in the display element of the present invention, thestate of the non-polar liquid changes based on the presence or absenceof an applied voltage and, by using a colored non-polar liquid, thedisplay element of the present invention is allowed to display, forexample, a colored state and a transparent state.

The voltage applied to the display element of the present invention isnot particularly restricted as long as it is such a voltage that canchange the state of the non-polar liquid.

The display element of the present invention may be an elementcomprising a single pixel region (cell) formed by compartmentalizing thehousing space with four partition walls or the like; however, it isusually an element comprising plural pixel regions that are formed bycompartmentalizing the housing space with plural partition walls, andeach pixel region is formed such that it is capable of performingfull-color display on the display surface side of the display element.Further, by allowing the state of the non-polar liquid in each pixelregion to be changed by an electrowetting phenomenon, the colorsdisplayed on the display surface side can be modified.

<Partition Wall>

The partition wall compartmentalizes the housing space formed betweenthe first and second electrode layer stacks. The partition wall is notparticularly restricted as long as it functions as a wall that preventsmovement of the non-polar liquid between adjacent pixel regions (cells)that usually exist in series.

Accordingly, the partition wall may be in contact with both the firstelectrode layer stack 11 and the second electrode layer stack 12 asshown in FIG. 1; however, when the non-polar liquid 14 exists on theside of the first electrode layer stack 11 in the housing space 16 asshown in FIG. 1, the partition wall may exist only on the side of thefirst stack 11 and does not have to be in contact with the secondelectrode layer stack 12.

When the partition wall is in contact with the first and/or secondelectrode layer stacks, the partition wall may be integrated with thefirst and/or second electrode layer stacks, or the partition wall may beadhered to the first and/or second electrode layer stacks.

The partition wall has a thermal linear expansion coefficient ofpreferably 0.1 to 150 ppm/K, more preferably 0.1 to 140 ppm/K, stillmore preferably 0.1 to 120 ppm/K, particularly preferably 0.1 to 100ppm/K. Specifically, the thermal linear expansion coefficient can bemeasured by the method described in the section of Examples below.

When the thermal linear expansion coefficient of the partition wall isin the above-described range, not only a display element in whichcracking or detachment between a partition wall and a layer in contacttherewith is not likely to occur can be obtained, but also the state ofa non-polar liquid contained therein can be changed smoothly and stablyover a prolonged period of time based on the presence or absence ofvoltage applied to the display element.

A partition wall having such a thermal linear expansion coefficient canbe obtained by appropriately adjusting the composition used for formingthe partition wall, specifically, by appropriately adjusting the amountof a cross-linkable monomer(s) to be used and/or the types and ratios ofa polymer and cross-linking agent used in the composition or byappropriately adjusting the amount of an inorganic filler to be used.For example, a partition wall having a low thermal linear expansioncoefficient can be obtained by increasing the amount of a cross-linkablemonomer to be used, the amount of a cross-linking agent to be used withrespect to the amount of a polymer, or the amount of an inorganic fillerto be used.

The height of the partition wall (length in the direction of the gapbetween the first and second electrode layer stacks; length in thevertical direction in FIG. 1) is not particularly restricted as long asthe partition wall can function to inhibit movement of the non-polarliquid between pixel regions.

Further, the thickness of the partition wall (length in the directionsubstantially perpendicular to the direction of the gap between thefirst and second electrode layer stacks; length in the horizontaldirection in FIG. 1) is also not particularly restricted as long as thepartition wall can function to inhibit the movement of the non-polarliquid; however, from the standpoints of the strength and the like ofthe partition wall, the thickness of the partition wall is 1 to 50 μm,preferably 5 to 40 μm.

The partition wall may be a single-layer film, or a laminate comprisinga BM (black matrix) layer, a reinforcement layer, a surface coatinglayer or the like. Further, the partition wall may be a film having nohole, or a film having lattice-form or slit-form holes.

[Photosensitive Composition]

It is preferred that the partition wall be a film obtained from aphotosensitive composition because, for example, this enables to easilyproduce a display element comprising plural pixel regions that areformed by compartmentalizing a housing space with plural partitionwalls.

It is more preferred that the partition wall be a film obtained from acomposition whose components are adjusted such that the thermal linearexpansion coefficient of the resulting partition wall is in theabove-described range. By using such a composition, not only a displayelement capable of smoothly and stably changing the state of a non-polarliquid contained therein over a prolonged period of time based on thepresence or absence of an applied voltage, in which the cracking ordetachment is not likely to occur, can be obtained, but also a partitionwall of a desired shape can be easily formed.

The above-described photosensitive composition may be a positivephotosensitive composition or a negative photosensitive composition;however, it is preferably a negative photosensitive composition because,for example, this enables to easily produce a display element comprisingplural pixel regions that are formed by compartmentalizing a housingspace with plural partition walls and a display element in whichreduction in display properties is not likely to occur over an extendedperiod can thus be obtained.

The photosensitive composition is not particularly restricted; however,it is preferably a composition comprising an alkali-soluble polymer, across-linking agent and a photoinitiator because, for example, such acomposition can yield a partition wall showing only small changes inproperties over a prolonged period of time. Examples of such acomposition include those described in JP-A-2006-154434 andJP-A-2007-293306.

The photosensitive composition can easily form a partition wall whichcompartmentalizes the first electrode layer stack, the second electrodelayer stack and a housing space that is formed between the first andsecond electrode layer stacks and comprises a polar liquid and anon-polar liquid that are immiscible with each other, wherein anabsolute value of the difference in thermal linear expansion coefficientbetween the partition wall and a surface layer is 150 ppm/K or less,preferably 130 ppm/K or less, more preferably 110 ppm/K or less,particularly preferably 100 ppm/K or less, the surface layer existing onthe surface of at least one of the first and second electrode layerstacks that is in contact with the housing space and being in contactwith the partition wall. Therefore, the photosensitive composition canbe suitably used as a composition for forming such a partition wall. Itis preferred that this photosensitive composition be a negativecomposition comprising an alkali-soluble polymer, a cross-linking agentand a photoinitiator.

<Alkali-Soluble Polymer>

The alkali-soluble polymer is not particularly restricted. In thepresent invention, the term “alkali-soluble” means that the polymer canbe dissolved in an alkaline solution, such as 2.38%-by-mass aqueoustetramethylammonium hydroxide solution.

The alkali-soluble polymer may be used individually, or two or morethereof, for example, a blend of an alkali-soluble polymer and analkali-insoluble polymer or a blend of two or more alkali-solublepolymers or the like, may be used.

From the standpoints of, for example, the solubility in alkalinesolutions, particularly 2.38%-by-mass aqueous tetramethylammoniumhydroxide solution, the alkali-soluble polymer is preferably a compoundhaving at least one functional group selected from the group consistingof a carboxyl group, a phenolic hydroxyl group and a silanol group.

As such an alkali-soluble polymer, an acrylic resin, polyimide,polybenzoxazole, polysiloxane, polyolefin, cardo skeleton-containingresin or novolac resin is preferred.

From the standpoints of the developability and the like of the resultingphotosensitive composition, the weight-average molecular weight of thealkali-soluble polymer, which is measured by gel permeation columnchromatography, specifically the method described in the section ofExamples below, is preferably 1,000 to 100,000, more preferably 1,500 to50,000.

From the standpoints of the developability and the like of the resultingphotosensitive composition, the content of the alkali-soluble polymer ispreferably 5 to 60% by mass, more preferably 10 to 50% by mass, withrespect to 100% by mass of the photosensitive composition.

Acrylic Resin

The acrylic resin is not particularly restricted; however, from thestandpoint of the alkali solubility, it is preferably one which has atleast one functional group selected from the group consisting of acarboxyl group, a phenolic hydroxyl group and a silanol group and, fromthe standpoints of the developability and the like of the resultingphotosensitive composition, it is preferably a copolymer obtained usingthe below-described compounds (a) and (b) as monomers (it is noted herethat the monomers include acrylic compounds):

compound (a): a compound having at least one functional group selectedfrom the group consisting of a carboxyl group, a phenolic hydroxyl groupand a silanol group; and

compound (b): a compound other than the compound (a).

In the compound (a), a compound having a carboxyl group is notparticularly restricted, and examples thereof include monocarboxylicacids such as acrylic acid, methacrylic acid and crotonic acid;dicarboxylic acids such as maleic acid, fumaric acid, citraconic acid,mesaconic acid and itaconic acid; and methacrylic acid derivativeshaving a carboxyl group and an ester bond, such as 2-maleinoloyloxyethylmethacrylate, 2-succinoloyloxyethyl methacrylate and2-hexahydrophthaloyloxyethyl methacrylate. These compounds may be usedindividually, or two or more thereof may be used. Thereamong, acrylicacid, methacrylic acid and 2-hexahydrophthaloyloxyethyl methacrylate arepreferred.

In the compound (a), a compound having a phenolic hydroxyl group is notparticularly restricted, and examples thereof include vinyl monomershaving a phenolic hydroxyl group, such as 3-hydroxystyrene,4-hydroxystyrene, vinyl-4-hydroxybenzoate, 3-isopropenylphenol and4-isopropenylphenol. These compounds may be used individually, or two ormore thereof may be used. Thereamong, 4-isopropenylphenol is preferred.

In the compound (a), a compound having a silanol group is notparticularly restricted, and examples thereof include hydrolysates ofalkoxysilyl group-containing vinyl monomers, such asvinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane,vinylmethyldimethoxysilane, vinylmethyldiethoxysilane,vinylmethyldipropoxysilane, γ-(meth)acryloxypropyltrimethoxysilane,γ-(meth)acryloxypropyltriethoxysilane,γ-(meth)acryloxypropyltripropoxysilane,γ-(meth)acryloxypropylmethyldimethoxysilane,γ-(meth)acryloxypropylmethyldiethoxysilane andγ-(meth)acryloxypropylmethyldipropoxysilane. These compounds may be usedindividually, or two or more thereof may be used.

Examples of the compound (b) include alkyl (meth)acrylates such asmethyl methacrylate, ethyl methacrylate, n-butyl (meth)acrylate,sec-butyl (meth)acrylate, t-butyl (meth)acrylate and isopropyl(meth)acrylate; alkoxy (meth)acrylates such as 2-ethoxyethyl(meth)acrylate and 2-methoxyethyl (meth)acrylate; hydroxylgroup-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate;halogen atom-containing (meth)acrylates such as 2,2,2-trifluoroethyl(meth)acrylate; aryl (meth)acrylates such as phenyl (meth)acrylate andbenzyl (meth)acrylate; heterocyclic group-containing (meth)acrylatessuch as glycidyl (meth)acrylate; dicarboxylic acid diesters such asdiethyl maleate, diethyl fumarate and diethyl itaconate; vinylgroup-containing aromatic compounds such as styrene, α-methylstyrene,m-methylstyrene, p-methylstyrene and p-methoxystyrene; conjugateddiolefins such as 1,3-butadiene, isoprene and 1,4-dimethylbutadiene;nitrile group-containing polymerizable compounds such as acrylonitrileand methacrylonitrile; chlorine-containing polymerizable compounds suchas vinyl chloride and vinylidene chloride; amide bond-containingpolymerizable compounds such as acrylamide and methacrylamide; imidegroup-containing polymerizable compounds such as N-phenylmaleimide;vinyl fatty acids such as vinyl acetate; and compounds represented bythe following Formulae (6) to (8).

[wherein, “n” independently represents a natural number of 1 to 6]

Thereamong, (meth)acrylates such as methyl methacrylate, ethylmethacrylate, n-butyl (meth)acrylate, 2-methoxyethyl acrylate and benzylmethacrylate; styrene, N-phenylmaleimide, 2-hydroxyethyl methacrylate,2,2,2-trifluoroethyl acrylate, glycidyl methacrylate and compoundsrepresented by the Formulae (6) and (7) are preferred.

The compound (b) may be used individually, or two or more thereof may beused.

The compound (b) is used in an amount of preferably 5 to 95% by mass,more preferably 10 to 90% by mass, with respect to a total of 100% bymass of the compounds (a) and (b).

The above-described acrylic resin can be obtained by, for example,polymerizing the compounds (a) and (b) in a conventionally known organicsolvent using a conventionally known radical initiator.

Polyimide

The polyimide is not particularly restricted; however, from thestandpoint of the alkali solubility, it is preferably one which has atleast one functional group selected from the group consisting of acarboxyl group, a phenolic hydroxyl group and a silanol group,particularly a polymer having the above-described functional group(s)and a structural unit represented by the following Formula (A1).

In the Formula (A1), R¹ represents a hydroxyl group-containing divalentgroup and X represents a tetravalent organic group. Examples of the R¹include divalent groups represented by the following Formula (a1).

In the Formula (a1), R² represents a single bond, an oxygen atom, asulfur atom, a sulfonyl group, a carbonyl group, a methylene group, adimethylmethylene group or a bis(trifluoromethyl)methylene group; andR³s independently represent a hydrogen atom, a formyl group, an acylgroup or an alkyl group. However, at least one of the R³s is a hydrogenatom. Further, “n1” and “n2” each independently represent an integer of0 to 2; however, at least one of “n1” and “n2” is 1 or 2. When the sumof “n1” and “n2” is 2 or larger, the plural R³s may be the same ordifferent.

Examples of the tetravalent organic group represented by the X includetetravalent aliphatic hydrocarbon groups, tetravalent aromatichydrocarbon groups, and groups represented by the following Formula (1).The X is preferably a tetravalent organic group derived from atetracarboxylic acid dianhydride, more preferably a group represented bythe following Formula (1).

In the Formula (1), Ars independently represent a trivalent aromatichydrocarbon group; and A represents a direct bond or a divalent group.Examples of the divalent group include an oxygen atom, a sulfur atom, asulfonyl group, a carbonyl group, a methylene group, a dimethylmethylenegroup and a bis(trifluoromethyl)methylene group.

The above-described polyimide can be obtained by a conventionally knownmethod, for example, imidization by a conventionally known method usinga diamine, an acid anhydride and the like.

In the polymer having a structural unit represented by the Formula (A1),the X or R¹ in the Formula (A1) may be at least one functional groupselected from the group consisting of a carboxyl group, a phenolichydroxyl group and a silanol group, and the polymer may be one which hasthe functional group(s) and is obtained by partial imidization using acompound having the functional group(s) as a raw material forsynthesizing the polymer.

The imidization ratio of the polyimide is preferably not less than 1%,more preferably not less than 3%, still more preferably not less than5%. The upper limit value of the imidization ratio may be 100%; however,it is preferably 50%, more preferably 30%. It is preferred that theimidization ratio be in this range because, for example, a polymerhaving excellent heat resistance and alkali solubility can be obtained.

The imidization ratio can be determined, for example, as follows.

First, the infrared absorption spectrum of the subject polyimide ismeasured and the presence of absorption peaks attributed to the imidestructure of the polyimide (near 1,780 cm⁻¹ and near 1,377 cm⁻¹) isconfirmed. Then, after heat-treating the polyimide for 1 hour at 350°C., the infrared absorption spectrum is measured again. The peakintensity near 1,377 cm⁻¹ is compared between before and after the heattreatment. Taking the post-heat treatment imidization ratio of thepolyimide as 100%, the pre-heat treatment imidization ratio of thepolyimide is determined by an equation: Pre-heat treatment imidizationratio={Pre-heat treatment peak intensity near 1,377 cm⁻¹/Post-heattreatment peak intensity near 1,377 cm⁻¹}×100(%). For the infraredabsorption spectrum measurements, for example, “NICOLET 6700FT-IR”(manufactured by Thermo Electron Co., Ltd.) is employed.

Polybenzoxazole

The polybenzoxazole is not particularly restricted; however, from thestandpoint of the alkali solubility, it is preferably one which has atleast one functional group selected from the group consisting of acarboxyl group, a phenolic hydroxyl group and a silanol group,particularly a polymer having the above-described functional group(s)and a structural unit represented by the following Formula (a5-1).

In the Formula (a5-1), X¹ represents an aromatic ring-containingtetravalent organic group, and Y¹ represents a divalent organic group.

In the Formula (a5-1), the aromatic ring of the X¹ may be either asubstituted or unsubstituted ring. Examples of a substituent include—OH, —COOH, alkyl groups, alkoxy groups and alicyclic hydrocarbongroups. N and O binding to the X¹ are, for example, bound to adjacentcarbon atoms on the aromatic ring of the X¹, forming a benzoxazole ring.When the X¹ contains two or more aromatic rings, the plural aromaticrings may form any of linked polycyclic and condensed polycyclicstructures.

The total number of carbon atoms of the X¹ is preferably 6 to 24, morepreferably 6 to 20, still more preferably 6 to 18.

In the Formula (a5-1), Y¹ is preferably a divalent group containing atleast one ring selected from alicyclic rings and aromatic rings, morepreferably a group having one to four aromatic rings, particularlypreferably a group having two aromatic rings.

The alicyclic ring(s) and/or aromatic ring(s) contained in the Y¹ mayeach be a substituted or unsubstituted ring. Examples of a substituentinclude —OH, —COOH, alkyl groups, alkoxy groups, alkoxycarbonyl groupsand alicyclic hydrocarbon groups. When the Y¹ contains two or more ofthe above-described rings, the plural rings may form any of linkedpolycyclic and condensed polycyclic structures.

The total number of carbon atoms of the Y¹ is preferably 4 to 24, morepreferably 4 to 15, still more preferably 6 to 12.

The above-described polybenzoxazole can be obtained by a conventionallyknown method, for example, polymerization of at least one selected fromdicarboxylic acids and their diesters and dihalides with a diaminehaving two hydroxyl groups.

In the polymer having a structural unit represented by the Formula(a5-1), the X¹ or Y¹ in the Formula (a5-1) may be at least onefunctional group selected from the group consisting of a carboxyl group,a phenolic hydroxyl group and a silanol group, and the polymer may beone which has the functional group(s) and is obtained by partialcyclization using a compound having the functional group(s) as a rawmaterial for synthesizing the polymer.

The cyclization ratio of the polybenzoxazole is preferably not less than1%, more preferably not less than 3%, still more preferably not lessthan 5%. The upper limit value of the cyclization ratio may be 100%;however, it is preferably 50%, more preferably 30%. It is preferred thatthe cyclization ratio be in this range because, for example, a polymerhaving excellent heat resistance and alkali solubility can be obtained.

The cyclization ratio can be determined, for example, as follows.

First, the infrared absorption spectrum of the subject polybenzoxazoleis measured and the presence of absorption peaks attributed to thebenzoxazole ring (near 1,557 cm⁻¹, 1,574 cm⁻¹) is confirmed. Then, afterheat-treating the polybenzoxazole for 1 hour at 350° C., the infraredabsorption spectrum is measured again. The peak intensity near 1,554cm⁻¹ is compared between before and after the heat treatment. Taking thepost-heat treatment cyclization ratio of the polybenzoxazole as 100%,the pre-heat treatment cyclization ratio of the polybenzoxazole isdetermined by an equation: Pre-heat treatment cyclizationratio={Pre-heat treatment peak intensity near 1,554 cm⁻¹/Post-heattreatment peak intensity near 1,554 cm⁻¹}×100(%). For the infraredabsorption spectrum measurements, for example, “NICOLET 6700FT-IR”(manufactured by Thermo Electron Co., Ltd.) is employed.

Polysiloxane

The polysiloxane is not particularly restricted; however, from thestandpoint of the alkali solubility, it is preferably one which has atleast one functional group selected from the group consisting of acarboxyl group, a phenolic hydroxyl group and a silanol group,particularly a polysiloxane which has the above-described functionalgroup(s) and is obtained by hydrolysis and partial condensation of anorganosilane represented by the following Formula (a4).

In the Formula (a4), R¹ represents a hydrogen atom, an alkyl grouphaving 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbonatoms, an aryl group-containing group having 6 to 15 carbon atoms, anepoxy ring-containing group having 2 to 15 carbon atoms or a groupobtained by replacing one or more hydrogen atoms contained in theabove-described alkyl group with a substituent (substituted alkyl group)and, when there are plural R¹s, the R¹s may be the same or differentfrom each other; R² represents a hydrogen atom, an alkyl group having 1to 6 carbon atoms, an acyl group having 1 to 6 carbon atoms or an arylgroup having 6 to 15 carbon atoms and, when there are plural R²s, theR²s may be the same or different from each other; and “n” represents aninteger of 0 to 3.

The above-described substituent is, for example, at least one selectedfrom halogen atoms, an amino group, a hydroxyl group, a mercapto group,an isocyanate group and a (meth)acryloyloxy group.

From the standpoint of allowing the partition wall to satisfy both crackresistance and hardness, the phenyl group content in the polysiloxane ispreferably 20 to 70 mol, more preferably 30 to 55 mol, with respect to100 mol of Si atoms. The phenyl group content can be measuredspecifically by the method described in the section of Examples below.

Polyolefin

The polyolefin is not particularly restricted; however, from thestandpoint of the alkali solubility, it is preferably one which has atleast one functional group selected from the group consisting of acarboxyl group, a phenolic hydroxyl group and a silanol group,particularly a cyclic olefin polymer having a protic polar group. Theterm “protic polar group” refers to an atomic group in which a hydrogenatom is directly bound to an atom belonging to the Group 15 or 16 of theperiodic table. The atom belonging to the Group 15 or 16 of the periodictable is preferably an oxygen atom, a nitrogen atom or a sulfur atom,particularly preferably an oxygen atom.

The cyclic olefin polymer refers to a homopolymer or copolymer of acyclic olefin having a cyclic structure, such as an alicyclic ring or anaromatic ring, and a carbon-carbon double bond. The cyclic olefinpolymer may also have a structural unit derived from a monomer otherthan the cyclic olefin.

From the standpoint of the alkali solubility, the cyclic olefin polymerhaving a protic polar group is preferably a polymer which has at leastone functional group selected from the group consisting of a carboxylgroup, a phenolic hydroxyl group and a silanol group and has astructural unit represented by, for example, the following Formula(A6-1), particularly the Formula (A6-1) and the Formula (A6-2).

In the Formula (A6-1), R^(a1) to R^(a4) each independently represent ahydrogen atom or —X_(n)—R^(a5) (wherein, X is a divalent organic group;n is 0 or 1; R^(a5) is an alkyl group, an aromatic group or theabove-described protic polar group, which alkyl group or aromatic groupmay have a substituent). At least one of the R^(a1) to R^(a4) is a—X_(n)—R^(a5) group wherein R^(a5) is the protic polar group. Further,“m” is an integer of 0 to 2, preferably 0 or 1.

Examples of the divalent organic group represented by the X includealkylene groups having 1 to 18 carbon atoms, such as a methylene groupand an ethylene group; and arylene groups having 6 to 24 carbon atoms,such as a phenylene group.

In the R^(a5), the alkyl group is, for example, a linear or branchedalkyl group having 1 to 18 carbon atoms, and the aromatic group is, forexample, an aromatic group having 6 to 24 carbon atoms.

In the Formula (A6-2), R^(b1) is a polar group other than the proticpolar group, preferably an acyloxy group having 2 to 12 carbon atomssuch as an acetoxy group, an alkoxycarbonyl group having 2 to 12 carbonatoms such as a methoxycarbonyl group, an ethoxycarbonyl group, ann-propoxycarbonyl group, an isopropoxycarbonyl group, ann-butoxycarbonyl group or a 2,2,2-trifluoroethoxycarbonyl group, anaryloxycarbonyl group having 7 to 24 carbon atoms such as aphenoxycarbonyl group, a cyano group, or a halogen atom such as achlorine atom.

R^(b2) is a hydrogen atom or an alkyl group having 1 to 18 carbon atomssuch as a methyl group.

R^(b3) and R^(b4) are hydrogen atoms.

It is noted here that the R^(b1) to R^(b4) in an arbitrary combination,together with two carbon atoms to which they are bound, may also form a3 to 5-membered heterocyclic structure containing an oxygen atom or anitrogen atom as a ring-constituting atom.

Further, “m” is an integer of 0 to 2, preferably 0 or 1.

The above-described polyolefin can be obtained by a conventionally knownmethod, for example, polymerization of a monomer which derives astructural unit represented by the Formula (A6-1). Further, the polymerobtained by the polymerization may be hydrogenated as well.

Cardo Skeleton-Containing Resin

The cardo skeleton-containing resin is not particularly restricted. The“cardo skeleton” refers to a skeletal structure in which two cyclicstructures are bound to a ring carbon atom constituting a cyclicstructure, and examples thereof include a structure in which twoaromatic rings (e.g., benzene rings) are bound to the carbon atom at the9-position of a fluorene ring.

As the cardo skeleton-containing resin, from the standpoint of thealkali solubility, it is preferred to use a resin having at least onegroup selected from a carboxyl group, a phenolic hydroxyl group and asilanol group.

Specific examples of the skeletal structure in which two cyclicstructures are bound to a ring carbon atom constituting a cyclicstructure include a 9,9-bis(phenyl)fluorene skeleton, a9,9-bis(hydroxyphenyl)fluorene skeleton, a 9,9-bis(cyanophenyl oraminoalkylphenyl)fluorene skeleton, an epoxy group-containing9,9-bis(phenyl)fluorene skeleton, and a (meth)acryl group-containing9,9-bis(phenyl)fluorene skeleton.

The cardo skeleton-containing resin can be obtained by a conventionallyknown method, for example, polymerization of a monomer having a cardoskeleton.

As the cardo skeleton-containing resin, a commercially available productcan be used as well. Examples thereof include polyester compounds havinga cardo skeleton, such as OGSOL CR-TR1, OGSOL CR-TR2, OGSOL CR-TR3,OGSOL CR-TR4, OGSOL CR-TR5 and OGSOL CR-TR6, all of which aremanufactured by Osaka Gas Chemicals Co., Ltd.

Novolac Resin

The novolac resin is not particularly restricted. Examples of thenovolac resin include resins having, for example, a phenol novolacstructure or a resol novolac structure, which are obtained by reactionbetween a phenol compound and an aldehyde compound.

As the novolac resin, one which is soluble to 2.38%-by-weighttetramethylammonium hydroxide is preferred.

The novolac resin is, for example, one having a structural unitrepresented by the following Formula (C1).

In the Formula (C1), A represents a phenolic hydroxyl group-containingdivalent aromatic group, and R¹ represents a methylene group, analkylene group having 2 to 30 carbon atoms, a divalent alicyclichydrocarbon group having 4 to 30 carbon atoms, an aralkylene grouphaving 7 to 30 carbon atoms or a group represented by —R²—Ar—R²—(wherein, Ar represents a divalent aromatic group; and R²s eachindependently represent a methylene group or an alkylene group having 2to 20 carbon atoms). Further, one of the hydrogen atoms of the methylenegroup may be substituted with a cyclopentadienyl group, an aromaticring, an aromatic ring-containing group, or a heterocycle having anitrogen atom, a sulfur atom, an oxygen atom or the like.

Regarding the R¹, examples of the group represented by —R²—Ar—R²—include a group represented by —CH₂-Ph-CH₂— (wherein, Ph is a phenylenegroup).

Regarding the A, the phenolic hydroxyl group-containing divalentaromatic group is, for example, a phenolic hydroxyl group-containingbenzene ring or a phenolic hydroxyl group-containing condensedpolycyclic aromatic group. The phenolic hydroxyl group-containingcondensed polycyclic aromatic group is, for example, a condensedpolycyclic aromatic hydrocarbon group in which some or all of thehydrogen atoms that are contained therein and bound to aromatic ringcarbons are substituted with hydroxyl groups. Examples of the condensedpolycyclic aromatic hydrocarbon group include a naphthalene ring, ananthracene ring and a phenanthrene ring.

The novolac resin can be obtained by a conventionally known methodusing, for example, phenol, formaldehyde and an acid catalyst or a basecatalyst. The novolac resin can also be obtained by the productionmethod described in, for example, Japanese Patent No. 2823057, JapanesePatent No. 3729554, Japanese Patent No. 3794598 or Japanese Patent No.3992181.

As the novolac resin, a commercially available product can be used aswell. Examples thereof include KAYARAD CCR-1291H and CCR-1235, which aremanufactured by Nippon Kayaku Co., Ltd.; and PR-40, PR-45, PR-80 andPR-85, which are manufactured by DIC Corporation.

<Cross-Linking Agent>

The above-described cross-linking agent is not particularly restrictedas long as it is a compound that has a cross-linkable functional groupand is capable of reacting with the above-described alkali-solublepolymer to form a cross-linked structure.

Examples of the cross-linkable functional group include an oxetanylgroup; epoxy group-containing groups such as a glycidyl ether group, aglycidyl ester group and a glycidyl amino group; alkoxyalkyl groups suchas a methoxymethyl group and an ethoxymethyl group; a benzyloxymethylgroup; an acetoxymethyl group; a benzoyloxymethyl group; a formyl group;an acetyl group; a dimethylaminomethyl group; a diethylaminomethylgroup; a dimethylolaminomethyl group; a diethylolaminomethyl group; amorpholinomethyl group; and ethylenically unsaturated groups such as avinyl group, a vinylidene group and a (meth)acryloyl group. Thereamong,the cross-linkable functional group is preferably an ethylenicallyunsaturated group, an epoxy group, an oxetanyl group or an alkoxyalkylgroup because, for example, a partition wall having excellent surfacehardness and showing only small changes in properties over an extendedperiod of time can be thereby obtained.

Examples of the above-described ethylenically unsaturatedgroup-containing compounds include compounds having at least twoethylenically unsaturated groups in the molecule, and preferred examplesthereof include compounds having two or more (meth)acryloyl groups.

Specific examples of such compounds include trimethylolpropanetri(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, butyleneglycol di(meth)acrylate, propylene glycol di(meth)acrylate,trimethylolpropane di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate,tris(2-hydroxyethyl)isocyanurate tri(meth)acrylate,tris(2-hydroxyethyl)isocyanurate di(meth)acrylate, tricyclodecanedimethanol di(meth)acrylate, cyclohexane dimethanol di(meth)acrylate,bisphenol A alkylene oxide di(meth)acrylate, (meth)acrylate obtained byadding (meth)acrylic acid to diglycidyl ether of bisphenol A, bisphenolA di(meth)acryloyloxyethyl ether, bisphenol Adi(meth)acryloyloxyethyloxyethyl ether, bisphenol Adi(meth)acryloyloxymethylethylether, bisphenol F alkyleneoxidedi(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate,tetramethylolpropane tetra(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate, dipentaerythritolhexa(meth)acrylate, glycerin tri(meth)acrylate, ethylene oxide-addedtrimethylolpropane tri(meth)acrylate, ethylene oxide-addedditrimethylolpropane tetra(meth)acrylate, ethylene oxide-addedpentaerythritol tetra(meth)acrylate, ethylene oxide-addeddipentaerythritol hexa(meth)acrylate, propylene oxide-addedtrimethylolpropane tri(meth)acrylate, propylene oxide-addedditrimethylolpropane tetra(meth)acrylate, propylene oxide-addedpentaerythritol tetra(meth)acrylate, propylene oxide-addeddipentaerythritol hexa(meth)acrylate, ε-caprolactone-addedtrimethylolpropane tri(meth)acrylate, ε-caprolactone-addedditrimethylolpropane tetra(meth)acrylate, ε-caprolactone-addedpentaerythritol tetra(meth)acrylate, and ε-caprolactone-addeddipentaerythritol hexa(meth)acrylate.

The above-described epoxy group or oxetanyl group-containing compoundsare not particularly restricted as long as they have an epoxy group oran oxetanyl group in the respective molecules, and examples thereofinclude KBM303 and KBM403 (both of which are manufactured by Shin-EtsuChemical Co., Ltd.); EPOLITE M-1230 and EPOLITE EHDG-L (both of whichare manufactured by Kyoeisha Chemical Co., Ltd.); PP-101 (manufacturedby Tohto Kasei Co., Ltd.); and NK OLIGO EA-1010/ECA (manufactured byShin-Nakamura Chemical Co., Ltd.).

Examples of a compound having two epoxy groups or oxetanyl groupsinclude EPOLITE 40E, EPOLITE 100E, EPOLITE 200E, EPOLITE 400E, EPOLITE70P, EPOLITE 200P, EPOLITE 400P, EPOLITE 1500NP, EPOLITE 80MF, EPOLITE4000 and EPOLITE 3002 (all of which are manufactured by KyoeishaChemical Co., Ltd.); NC6000 (manufactured by Nippon Kayaku Co., Ltd.);DENACOL EX-212L, DENACOL EX-214L, DENACOL EX-216L and DENACOL EX-850L(all of which are manufactured by Nagase ChemteX Corporation); CELLOXIDE2021P (manufactured by Daicel Chemical Industries, Ltd.); GAN and GOT(both of which are manufactured by Nippon Kayaku Co, Ltd.); jER828,jER1002, jER1750, jER1007, YX8100-BH30, E1256, E4250 and E4275 (all ofwhich are manufactured by Mitsubishi Chemical Corporation); BPFG, BPEFGand OGSOL PG100 (all of which are manufactured by Osaka Gas ChemicalsCo., Ltd.); EPICLON EXA-9583 and HP4032 (both of which are manufacturedby DIC Corporation); and EP-4088S, EP-4085S and EP-4080S (all of whichare manufactured by ADEKA Corporation).

Examples of a compound having three epoxy groups or oxetanyl groupsinclude VG3101 (manufactured by Mitsui Chemicals, Inc.); TEPIC S, TEPICG and TEPIC P (which are manufactured by Nissan Chemical Industries,Ltd.); and DENACOL EX-321L (manufactured by Nagase ChemteX Corporation).

Examples of a compound having four or more epoxy groups or oxetanylgroups include EPOTOHTO YH-434L (manufactured by Tohto Kasei Co., Ltd.);EPPN502H, NC3000 and NC6000 (all of which are manufactured by NipponKayaku Co., Ltd.); and EPICLON N695 and HP7200 (both of which aremanufactured by DIC Corporation).

Examples of the oxetanyl group-containing compound include4,4-bis[(3-ethyl-3-oxetanyl)methyl]biphenyl,3,7-bis(3-oxetanyl)-5-oxanonane,3,3′-[1,3-(2-methylenyl)propanediylbis(oxymethylene)]bis(3-ethyloxetane),1,4-bis[(3-ethyl-3-oxetanyl)methoxymethyl]benzene,1,2-bis[(3-ethyl-3-oxetanyl)methoxymethyl]ethane,1,3-bis[(3-ethyl-3-oxetanyl)methoxymethyl]propane, ethyleneglycol-bis[(3-ethyl-3-oxetanyl)methyl]ether,dicyclopentenyl-bis[(3-ethyl-3-oxetanyl)methyl]ether, triethyleneglycol-bis[(3-ethyl-3-oxetanyl)methyl]ether, tetraethyleneglycol-bis[(3-ethyl-3-oxetanyl)methyl]ether,tricyclodecanediyldimethylene-bis[(3-ethyl-3-oxetanyl)methyl]ether,trimethylolpropane tris[(3-ethyl-3-oxetanyl)methyl]ether,1,4-bis[(3-ethyl-3-oxetanyl)methoxy]butane,1,6-bis[(3-ethyl-3-oxetanyl)methoxy]hexane, pentaerythritoltris[(3-ethyl-3-oxetanyl)methyl]ether, pentaerythritoltetrakis[(3-ethyl-3-oxetanyl)methyl]ether, polyethyleneglycol-bis[(3-ethyl-3-oxetanyl)methyl]ether, dipentaerythritolhexakis[(3-ethyl-3-oxetanyl)methyl]ether, dipentaerythritolpentakis[(3-ethyl-3-oxetanyl)methyl]ether, and dipentaerythritoltetrakis[(3-ethyl-3-oxetanyl)methyl]ether.

The alkoxyalkyl group-containing compounds are not particularlyrestricted as long as they have an alkoxyalkyl group in the respectivemolecules, and examples thereof include alkoxyalkyl group-containingmelamine compounds, alkoxyalkyl group-containing benzoguanaminecompounds, alkoxyalkyl group-containing urea compounds, and alkoxyalkylgroup-containing phenol compounds.

The above-described cross-linking agents may be used individually, ortwo or more thereof may be used.

From the standpoints of, for example, obtaining a composition havingexcellent photosensitivity and a partition wall showing only smallchanges in properties over a prolonged period of time, the content ofthe cross-linking agent(s) is preferably 5 to 80% by mass, morepreferably 10 to 70% by mass, particularly preferably 15 to 60% by mass,with respect to 100% by mass of the photosensitive composition.

<Photoinitiator>

The above-described photoinitiator is not particularly restricted aslong as it is a compound which leads to initiate polymerization byirradiating with light such as radiation, and a conventionally knowncompound can be used as the photoinitiator.

Examples of such a compound include2,2′-bis(2,4-dichlorophenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2-chlorophenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2,4-dimethylphenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazole,2,2′-bis(2-methylphenyl)-4,5,4′,5′-tetraphenyl-1,2′-biimidazole,2,2′-diphenyl-4,5,4′,5′-tetraphenyl-1,2′-biimidazole,diethoxyacetophenone,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone,2,2-dimethoxy-1,2-diphenylethane-1-one, benzoin, benzophenone, methylo-benzoylbenzoate, 4-phenylbenzophenone,4,4′-bis(diethylamino)benzophenone,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropane-1,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone1-(O-acetyloxime), 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide,2,4-bis(trichloromethyl)-6-(4-methoxyphenyl)-1,3,5-triazine, and2,4-bis(trichloromethyl)-6-(4-methoxynaphthyl)-1,3,5-triazine.

The above-described photoinitiators may be used individually, or two ormore thereof may be used.

From the standpoints of, for example, obtaining a composition havingexcellent photosensitivity, the content of the photoinitiator(s) ispreferably 0.1 to 20% by mass, more preferably 0.5 to 10% by mass, withrespect to 100% by mass of the photosensitive composition. Bycontrolling the content of the photoinitiator(s) in this range, thedevelopability of the partition wall formed from the photosensitivecomposition tends to be improved without impairing the sensitivity.

In the photosensitive composition, other additives such as an organicsolvent, an antioxidant, a thermal polymerization inhibitor, asurfactant, an adhesive assistant, a solubility modifier, a viscositymodifier, a filler (e.g., an inorganic filler) and a colorant can befurther incorporated within a range that does not adversely affect theeffects of the present invention.

Examples of the organic solvent include those described inJP-A-2006-201670, JP-A-2012-256023, JP-A-2014-013413 and the like.

Examples of the antioxidant include those described in JP-A-2010-117614,JP-A-2010-184961, JP-A-2013-241554 and the like.

Examples of the surfactant include those described in JP-A-2010-250109,JP-A-2014-089970, JP-A-2014-048428 and the like.

Examples of the adhesive assistant include those described inJP-A-2012-256023, JP-A-2013-242511, JP-A-2014-080578 and the like.

Examples of the inorganic filler include those described inJP-A-2007-332255, JP-A-2008-242076, JP-A-2012-198527, JP-A-2013-216737,JP-A-2014-062195 and the like.

Examples of other additives include those compounds that are describedin JP-A-2006-154434, JP-A-2007-293306 and the like.

<Method of Preparing Photosensitive Composition>

The photosensitive composition can be prepared by, for example, mixingan alkali-soluble polymer, a cross-linking agent, a photoinitiator andother arbitrary additive(s). Further, in order to remove contaminants,after uniformly mixing these components, the resulting mixture may besubjected to filtration using a filter or the like.

[Method of Forming Partition Wall]

The method of forming the partition wall is not particularly restrictedand, for example, a method of forming a partition wall by coating andcuring the above-described photosensitive composition can be preferablyemployed.

Such a partition wall-forming method may be carried out directly on thefirst or second electrode layer stack, or it may be carried out on othersupport such as a glass support, a metal support or a resin support andthe resulting partition wall may then be arranged on the first or secondelectrode layer stack; however, it is preferably carried out directly onan electrode layer stack having the above-described surface layer.

The method of forming the partition wall is not particularly restricted;however, specifically, the partition wall can be obtained by coating thephotosensitive composition on the first or second electrode layer stackor other support, drying the coated photosensitive composition asrequired and then curing the photosensitive composition by irradiationwith light. Here, by performing the irradiation with light (exposure)using a mask having a prescribed pattern, subsequently developing thephotosensitive composition with an alkaline developer and, as required,heating the resultant, a partition wall of a desired shape such as alattice shape can be obtained, and this enables to easily produce adisplay element having plural pixel regions that are formed bycompartmentalizing the housing space with plural partition walls.

These processes can be carried out by a conventionally known method,examples of which include the method described in JP-A-2012-256023.

A surface, preferably both surfaces of the partition wall obtained bythe above-described method may be further subjected to a surfacetreatment which, for example, hydrophilizes the surface(s) by aconventionally known hydrophilization method or hydrophobizes thesurface(s) by a conventionally known hydrophobization method.

Examples of the hydrophilization treatment method include a method ofmodifying the surface of the obtained film by a corona dischargetreatment, a plasma treatment or an UV-ozone treatment; and a method oflayering a film comprising of an acrylic resin, a sulfonategroup-containing resin or the like on the surface of the obtained filmby coating or lamination.

Examples of the hydrophobization treatment method include a method ofmodifying the surface of the obtained film by treatment with along-chain alkyl group-containing coupling agent, a fluorine-containingcoupling agent or a silicon-containing coupling agent; and a method oflayering a film comprising of a long-chain alkyl group-containing resin,a fluorine-containing resin, a silicon-containing resin or the like onthe surface of the obtained film by coating or lamination.

For example, in cases where a film is formed from the photosensitivecomposition and the surface of the film is subjected to an UV-ozonetreatment, the exposure dose in this treatment is preferably 0.1 to 8J/cm² @ 254 nm, more preferably 0.5 to 5 J/cm² @ 254 nm, because, forexample, this enables to easily obtain a partition wall havinghydrophilicity, light resistance, heat resistance, chemical resistanceand high hardness.

<First Electrode Layer Stack and Second Electrode Layer Stack>

The first and second electrode layer stacks are not particularlyrestricted; however, they are each preferably a stack (laminate)composed of a transparent material.

The first and second electrode layer stacks usually comprise: atransparent substrate made of glass or resin; and a transparentelectroconductive layer composed of a transparent electroconductivematerial such as indium tin oxide (ITO).

When such electrode layer stacks are used, they are arranged such thattheir transparent electroconductive layer sides face with each other.

The first and second electrode layer stacks may further comprise otherlayer(s), for example, a conventionally known layer(s) such as aplanarization film, a passivation film, a reflective film, an insulationfilm and/or a hydrophobic film, on the transparent substrate ortransparent electroconductive layer or therebetween.

The first and second electrode layer stacks comprise the above-describedlayer(s) and, among these layers, a layer which exists on the surface incontact with the housing space and is in contact with the partitionwall, the layer existing on the surface of at least one of the electrodelayer stacks, is the surface layer of the present invention.

In the present invention, using a layer conforming to the propertiesdesired in the resulting display element as the surface layer and takinginto consideration the thermal linear expansion coefficient of thislayer, a partition wall-forming composition may be prepared and apartition wall may be formed therefrom. Alternatively, using a partitionwall conforming to the desired properties and taking into considerationthe thermal linear expansion coefficient of this partition wall, thesurface layer may be arranged on the surface of at least one of theelectrode layer stacks.

It is preferred that the surface layer be a hydrophobic layer. The twosurfaces of the first and second electrode layer stacks that are incontact with the housing space may both be hydrophobic layers; however,in that case, it is preferred that these surfaces have different levelsof hydrophobicity, with the hydrophobicity of one of the surfaces beinghigher than that of the other surface.

In other words, in the display element of the present invention, it ispreferred that the first and second electrode layer stacks have suchhydrophobic layers that, when no voltage is applied between the firstand second electrode layer stacks, allow the non-polar liquid to existon the surface of at least one of the first and second electrode layerstacks that is in contact with the housing space.

An electrode layer stack having the above-described hydrophobic layercan be obtained by, for example, on the surface of a laminate comprisinga transparent substrate and a transparent electroconductive layer,coating a hydrophobic material-containing composition to form a coatingfilm or laminating a film composed of a hydrophobic material.

Examples of the hydrophobic material include fluorine-containingmaterials and silicon-containing materials, among whichfluorine-containing materials are preferred.

Examples of the fluorine-containing materials include fluorocarbonpolymers described in JP-A-2011-157292, JP-A-2010-121137,JP-A-2003-315308, Japanese Patent No. 4045253, JP-A-2013-142753,JP-T-2013-522669 and JP-A-2014-066835.

Further, as a fluorine-containing material, a product that iscommercially available on the market may be used as well, and examplesthereof include CYTOP manufactured by Asahi Glass Co., Ltd. (trade name:CTL-809M) and TEFLON (registered trademark) manufactured by DuPont Co.(trade name: AF1600 and AF2400).

<Housing Space>

The housing space may be a space of any size as long as it can contain apolar liquid and a non-polar liquid and does not interfere with thechange in the state of the non-polar liquid based on the presence orabsence of an applied voltage. The housing space can be selected asappropriate in accordance with the desired application as well as thesize and the like of the pixel regions desired to be displayed.

<Polar Liquid>

The polar liquid is stored in the housing space. The polar liquid is notparticularly restricted as long as it is immiscible with the non-polarliquid to be used; however, it is preferably an electroconductive liquidthat is colorless and transparent. Specifically, as the polar liquid, inaddition to water, an aqueous solution or the like in which anelectrolyte such as lithium chloride, potassium chloride or sodiumchloride is dissolved can be used.

As the polar liquid, two or more kinds of liquid may be used; however, asingle kind of liquid is usually used.

<Non-Polar Liquid>

The non-polar liquid is also stored in the housing space. The non-polarliquid is not particularly restricted; however, it is preferably aliquid that is hardly polar and shows electrical insulation.

Examples of the non-polar liquid include hydrophobic liquids such asside-chain higher alcohols, side-chain higher fatty acids, alkanehydrocarbons such as octane and decane, and silicone oil.

As the non-polar liquid, two or more kinds of liquid may be used;however, a single kind of liquid is usually used.

The amount of the non-polar liquid to be stored in each pixel region(cell) can be adjusted as appropriate in accordance with the desiredapplication; however, it is preferably, for example, such an amount thatcan cover the entire surface of the electrode layer stack on the displaysurface side of the display element.

The non-polar liquid used in the present invention is preferably aliquid having a color (colored liquid), particularly the above-describedhydrophobic liquid in which a color material that can be dissolved oruniformly dispersed therein, such as a dye or a pigment, is blended. Thecolored liquid may be transparent or opaque.

Examples of the dye include those described in JP-A-2014-010249 andJP-A-2013-228683, and examples of the pigment include carbon blacks andpigments described in JP-A-2012-181513.

As the color material, one which allows the non-polar liquid to absorblight having a prescribed wavelength can be selected as appropriate inaccordance with the desired application, and such a color material maybe used individually, or two or more thereof may be used.

When the non-polar liquid contains a color material, the content thereofis not particularly restricted and can be adjusted as appropriate inaccordance with the desired application; however, it is preferred thatthe color material be contained in such an amount that can be dissolvedor uniformly dispersed in the hydrophobic liquid, for example, 0.01 to30% by mass with respect to 100% by mass of the non-polar liquid.

Further, as required, the non-polar liquid may also contain a variety ofadditives, such as an ultraviolet absorber and an antioxidant, within arange that does not adversely affect the effects of the presentinvention.

<<Electrowetting Display>>

The electrowetting display of the present invention is not particularlyrestricted as long as it comprises the above-described display elementof the present invention.

Since the electrowetting display of the present invention comprises thedisplay element of the present invention, it has a long service life andexcellent display properties.

The electrowetting display of the present invention can be produced bylaminating conventionally known layers that have been used inconventional electrowetting displays, such as an insulation film, athin-film transistor (TFT), a color filter layer and a black matrix, atthe desired place in the desired order in accordance with the desiredapplication. Such a constitution of the electrowetting display may bethe same as, for example, the one described in JP-A-2013-142753 orJP-A-2012-63767, except that the display element of the presentinvention is used.

Particularly, it is preferred that the electrowetting display of thepresent invention contain a color filter layer because, for example,this enables to produce a display capable of performing full-colordisplay on the display surface side at a low cost.

The color filter layer is not particularly restricted. The color filterlayer is not restricted to a red, blue or green layer, and a layerhaving a color of cyan, magenta, yellow or the like can also be selectedas appropriate in accordance with the desired application.

Further, the color filter layer can be arranged at any desired positionin accordance with the desired application and, for example, when theelectrowetting display of the present invention comprises a color filterlayer and a TFT, the color filter layer may be arranged on the side ofthe display element of the present invention on which the TFT islaminated or on the opposite side thereof.

EXAMPLES

Embodiments of the present invention will now be described moreconcretely by way of examples thereof. However, the present invention isnot restricted thereto by any means. It is noted here that, unlessotherwise specified, “part(s)” and “%” are all based on mass.

The weight-average molecular weights (Mw) of the polymers obtained inthe below-described Synthesis Examples were measured by gel permeationcolumn chromatography under the following conditions.

-   -   Measurement method: gel permeation chromatography    -   Standard substance: polystyrene    -   Apparatus: manufactured by Tosoh Corporation, trade name:        HLC-8020    -   Column: A column prepared by sequentially connecting Guard        Column H_(XL)-H, TSK gel G7000H_(XL), 2×TSK gel GMH_(XL), and        TSK gel G2000H_(XL).        These columns are manufactured by Tosoh Corporation.    -   Solvent: tetrahydrofuran    -   Sample concentration: 0.7% by mass    -   Injection volume: 70 μL    -   Flow rate: 1 mL/min

1. Synthesis of Polymers [Synthesis Example 1] Synthesis of Polymer (A1)

To a reaction vessel, 160 parts of propylene glycol monomethyl etheracetate (PGMEA) was loaded, and the temperature thereof was raised to80° C. To the resulting reaction vessel, 13 parts of methacrylic acid,46 parts of benzyl methacrylate, 13 parts of styrene, 16 parts ofN-phenylmaleimide, 2 parts of n-butyl methacrylate and 10 parts of2-hydroxyethyl methacrylate, which were used as monomers, and a solutionobtained by mixing 5 parts of azobis-2,4-dimethylvaleronitrile as apolymerization catalyst and 25 parts of PGMEA as a solvent were eachadded dropwise over a period of 2 hours. Thereafter, the resulting mixedsolution was heated at 80° C. for 2 hours and then at 100° C. for 1hour. The thus heated mixed solution was allowed to cool to 23° C.,thereby obtaining a PGMEA solution containing a polymer (A1) at a solidconcentration of 35% by mass. The thus obtained polymer (A1) had a Mw of12,000.

Synthesis Example 2 Synthesis of Polymer (A2)

To a reaction vessel, 90 parts of PGMEA was loaded, and the temperaturethereof was raised to 80° C. To the resulting reaction vessel, asolution obtained by mixing 20 parts of methacrylic acid, 40 parts ofbenzyl methacrylate and 10 parts of 2-hydroxyethyl methacrylate asmonomers with 15 parts of PGMEA as a solvent and a solution obtained bymixing 6 parts of azobis-2,4-dimethylvaleronitrile as a polymerizationcatalyst and 25 parts of PGMEA as a solvent were each added dropwiseover a period of 2 hours. Thereafter, the resulting mixed solution washeated at 80° C. for 2 hours and then at 100° C. for 1 hour. Afterallowing the thus heated mixed solution to cool to 23° C., 30 parts ofglycidyl methacrylate and 1 part of tetra-n-butylammonium chloride werefurther added, and the resultant was heated at 80° C. for 12 hours. Thethus heated mixed solution was allowed to cool to 23° C., therebyobtaining a PGMEA solution containing a polymer (A2) at a solidconcentration of 35% by mass. The thus obtained polymer (A2) had a Mw of20,000.

[Synthesis Example 3] Synthesis of Polymer (A3) (Polyimide)

To a three-necked flask, 390 g of γ-butyrolactone (γ-BL) was added as apolymerization solvent, and 120 g of2,2′-bis(3-amino-4-hydroxyphenyl)hexafluoropropane was added as adiamine compound to the polymerization solvent. After dissolving thediamine compound to the polymerization solvent, 71 g of4,4′-oxydiphthalic dianhydride was added thereto as an acid dianhydride.Then, after allowing the resulting mixture to react at 60° C. for 1hour, 19 g of maleic anhydride was added as an end-capping agent. Theresultant was further allowed to react at 60° C. for 1 hour and then atan increased temperature of 180° C. for 4 hours, thereby obtaining about600 g of γ-BL solution containing a polymer (A3) at a solidconcentration of 35% by mass. The thus obtained polymer (A3) had a Mw of8,000.

[Synthesis Example 4] Synthesis of Polymer (A4) (PolybenzoxazolePrecursor)

To a four-necked separable flask equipped with a thermometer, a stirrer,a material inlet port and a dry nitrogen gas-introducing tube, 443.2 g(0.90 mol) of dicarboxylic acid derivative, which was obtained byallowing 1 mol of diphenyl ether-4,4′-dicarboxylic acid to react with 2mol of 1-hydroxybenzotriazole, and 366.3 parts (1.00 mol) ofhexafluoro-2,2-bis(3-amino-4-hydroxyphenyl)propane were loaded, and3,000 parts of N-methyl-2-pyrrolidone was added and dissolved thereto.Then, using an oil bath, the resulting mixture was allowed to react at75° C. for 16 hours. Thereafter, 32.8 parts (0.20 mol) of5-norbornene-2,3-dicarboxylic acid anhydride dissolved in 100 parts ofN-methyl-2-pyrrolidone was added, and the resulting mixture was furtherstirred for 3 hours and the reaction was terminated. After subjectingthe reaction mixture to filtration, the cake was added to a solution ofwater and isopropanol (water/isopropanol=3/1 (mass ratio)), and theresulting precipitates were recovered by filtration, sufficiently washedwith water and then dried under vacuum to obtain a polybenzoxazoleprecursor (polymer (A4)). By adding γ-BL thereto to a polymer (A4)concentration of 35% by mass, a γ-BL solution of the polymer (A4) wasobtained. The thus obtained polymer (A4) had a Mw of 15,000.

[Synthesis Example 5] Synthesis of Polymer (A5) (Polysiloxane)

To a 500-mL three-necked flask, 63.39 parts (0.55 mol) ofmethyltrimethoxysilane, 69.41 parts (0.35 mol) ofphenyltrimethoxysilane, 24.64 parts (0.1 mol) of2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and 150.36 parts ofpropylene glycol monomethyl ether (PGME) were loaded and, while stirringthe loaded materials at room temperature, an aqueous phosphoric acidsolution prepared by dissolving 0.338 part of phosphoric acid (0.2% bymass with respect to the loaded monomers) in 55.8 parts of water wasadded over a period of 10 minutes. After stirring the resulting mixturefor 1 hour with the flask being immersed in a 70° C. oil bath, the oilbath was heated to 115° C. over a period of 30 minutes. The innertemperature of the flask reached 100° C. one hour after the start of theheating and, from that point on, the flask was heated with stirring for2 hours (the inner temperature of the flask was 100 to 110° C.). Duringthe reaction, methanol and water, which were by-products, weredistillated in a total of 115 parts. To the resulting PGME solution ofpolymer (A5), PGME was further added to a polymer (A5) concentration of35% by mass, thereby obtaining a PGME solution of the polymer (A5). Thethus obtained polymer (A5) had a Mw of 5,000 and a phenyl group contentof 35 mol with respect to 100 mol of Si atoms.

The phenyl group content in the polymer (A5) was determined by measuringthe ²⁹Si-nuclear magnetic resonance spectrum of the polymer (A5) using“JNM-ECS 400” (manufactured by JEOL Ltd.) and calculating the ratiobetween the peak area of phenyl group-bound Si and that of Si not boundwith a phenyl group.

[Synthesis Example 6] Synthesis of Polymer (A6) (Polyolefin)

To a nitrogen-substituted 1,000-mL autoclave, 60 parts of8-carboxytetracyclo[4.4.0.1^(2,5).1^(7,10)]dodeca-3-ene, 40 parts ofN-phenyl-(5-norbornene-2,3-dicarboxyimide), 2.8 parts of 1,5-hexadiene,0.05 part of (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine) benzylidene ruthenium dichloride and 400 partsof PGMEA were loaded and, under stirring, the loaded materials wereallowed to undergo polymerization reaction at 80° C. for 2 hours toobtain a polymer solution containing a polymer (A6′).

To this polymer solution, 0.1 part ofbis(tricyclohexylphosphine)ethoxymethylene ruthenium dichloride wasadded as a hydrogenation catalyst, and hydrogen was blown into theresulting solution for 5 hours at a pressure of 4 MPa to allowhydrogenation reaction to progress. Then, 1 part of powdered activatedcarbon was added and, under stirring, hydrogen was blown into theresulting solution for 3 hours at a temperature of 150° C. and apressure of 4 MPa. Thereafter, the activated carbon was separated byfiltration using a fluorocarbon resin-made filter having a pore size of0.2 μm to obtain 490 parts of a hydrogenation reaction solutioncontaining a polymer (A6), which is a hydride of the polymer (A6′). Thethus obtained polymer (A6)-containing hydrogenation reaction solutionhad a solid concentration of 21% by mass and the yield of the polymer(A6) was 102 parts. This polymer (A6)-containing hydrogenation reactionsolution was concentrated using a rotary evaporator to adjust the solidconcentration to 35% by mass, thereby obtaining a solution of thepolymer (A6). The thus obtained polymer (A6) had a Mw of 4,000.

[Preparation Example 7] Preparation of Polymer (A7) (Cardo Resin)

CR-TR5 (manufactured by Osaka Gas Chemicals Co., Ltd.), which is a PGMEsolution of a cardo resin, is a product having a solid content of 52.7%by mass and a solid acid value of 135 KOH mg/g. Here, 100 parts ofCR-TR5 was weighed, 50.57 parts of PGME was added thereto, and theresultant was stirred. In this manner, a cardo resin (A7) solutionhaving a solid concentration of 35% by mass was obtained.

[Synthesis Example 8] Synthesis of Polymer (A8) (Novolac Resin)

To a flask equipped with a thermometer, a condenser, a fractionatingcolumn and a stirrer, 94.1 g (1.0 mol) of phenol, 400 g of methylisobutyl ketone, 96 g of water and 32.6 g (1.0 mol in terms offormaldehyde) of 92%-by-mass paraformaldehyde were loaded. Subsequently,while stirring the loaded materials, 3.4 g of p-toluenesulfonic acid wasadded thereto, and the resultant was allowed to react at 100° C. for 8hours. After completion of the reaction, 200 g of pure water was added,and the resulting solution in the system was transferred to a separatoryfunnel to separate and remove the aqueous layer. Then, after washing theorganic layer with water until the water after washing became neutral,the solvent was removed from the organic layer under heating and reducedpressure to obtain 140 g of a novolac resin (polymer (A8)). The thusobtained polymer (A8) had a Mw of 2,000. Using this polymer (A8) andPGMEA, a polymer (A8) solution having a solid concentration of 35% bymass was obtained.

From a measurement chart obtained using a Fourier-transform infrared(FT-IR) spectrophotometer, in comparison to the raw materials,absorption attributed to stretching caused by methylene bond (2,800 to3,000 cm⁻¹) was confirmed; however, absorption attributed to aromaticether (1,000 to 1,200 cm⁻¹) was not found. From these results, in thisSynthesis Example, it can be determined that nodehydration-etherification reaction between hydroxyl groups (loss ofhydroxyl groups) occurred and that a novolac resin having a methylenebond was obtained.

2. Preparation of Photosensitive Compositions for Formation of PartitionWall

Composition 1 in the form of a solution was obtained by mixing 100 parts(in terms of the polymer (A1)) of the polymer (A1) solution obtained inSynthesis Example 1, 50 parts of a cross-linking agent (B2), 5 parts ofa photoinitiator (C), 5 parts of an adhesive assistant (D) and 1 part ofa surfactant (E).

Compositions 2 to 14 were also obtained in the same manner by mixing therespective components in accordance with the formulations shown in Table1 below. In the compositions 2 to 14 as well, the polymer solutionobtained above was used such that each composition contained the polymerin the amount shown in Table 1. The details of each component in Table 1are as shown in Table 2 below.

TABLE 1 Com- Com- Com- Com- Com- Com- Com- Com- posi- posi- posi- posi-posi- posi- posi- posi- Composi- Composi- Composi- Composi- Composi-Composi- tion 1 tion 2 tion 3 tion 4 tion 5 tion 6 tion 7 tion 8 tion 9tion 10 tion 11 tion 12 tion 13 tion 14 Polymer A1 100 100 100 100 A2100 100 100 100 A3 100 A4 100 A5 100 A6 100 A7 100 A8 100 Cross-linkingB1 0 0 0 50 100 100 100 100 100 100 100 100 100 30 agent B2 50 70 100 500 0 0 0 0 0 0 0 0 0 Photoinitiator C 5 5 4 6 6 6 6 6 6 6 6 6 6 5Adhesive D 5 5 5 5 5 5 5 5 5 5 5 5 5 5 assistant Surfactant E 1 1 1 1 11 1 1 1 1 1 1 1 1 Inorganic F 0 0 0 0 0 5 15 0 0 0 0 0 0 0 filler

TABLE 2 B1 Dipentaerythritol hexaacrylate B2 1,9-nonanediol diacrylate C1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]ethanone 1-(O-acetyloxime) (trade name “IRGACURE Oxe02”, manufactured by BASF) DMethacryloxypropyltrimethoxysilane (trade name “XIAMETER OFS-6030SILANE”, manufactured by Dow Corning Toray, Co., Ltd.) E Fluorinesurfactant (trade name “FTX-218F”, manufactured by Neos Co., Ltd.) FZirconia particle (trade name “SZR-M”, manufactured by Sakai ChemicalIndustry Co., Ltd.)

Example 1 3. Preparation of Partition Wall

On a 100 nm-thick ITO layer provided on one side of a glass wafer, thecomposition 1 shown in Table 1 was coated and then heat-treated at 110°C. for 5 minutes on a hot plate (pre-baking) to form a coating film of25 to 35 μm in height (length in the direction corresponding to thevertical direction in FIG. 1). Using a stepper (model “NSR-2005i10D”,manufactured by Nikon Corporation), the thus formed coating film wasexposed through a patterned mask at the UV dose shown in Table 3. Thethus exposed coating film was immersed in an aqueous solution containing2.38% by mass of tetramethylammonium hydroxide for 90 seconds(development process) and subsequently washed with water. Then, afterheat-treating the resulting coating film in an oven at 220° C. for 1hour, the surface of the coating film was subjected to an UV-ozonetreatment by a low-pressure mercury lamp (exposure dose: 3 J/cm²@ 254nm) using a table-top light surface processor (trade name: PL16-110,manufactured by SEN Lights Co., Ltd.), thereby preparing a partitionwall (lattice-patterned coating film) having a line width of 10 μm, alattice spacing of 50 μm and a height (length in the directioncorresponding to the vertical direction in FIG. 1) of 20 μm. The planview of the thus obtained partition wall (lattice-patterned coatingfilm) is shown in FIG. 2.

It is noted here that, in the present invention, the value of exposuredose (J/cm² @ 254 nm) is the dose of the irradiated ultravioletradiation that was converted into the amount of light having awavelength of 254 nm and the value of exposure dose (mJ/cm² @ 365 nm) isthe dose of the irradiated ultraviolet radiation that was converted intothe amount of light having a wavelength of 365 nm.

4. Preparation of Display Element

A partition wall having a height (length in the direction correspondingto the vertical direction in FIG. 1) of 20 μm, a line width of 10 μm anda lattice spacing of 50 μm was formed in the same manner as in the above“3. Preparation of Partition Wall”, except that a 0.7 mm-thick glassplate having a 100 nm-thick ITO layer on one side and a 450 μm-thickhydrophobic film thereon (amorphous fluorine-containing polymer“AF1600”, manufactured by DuPont Co.) was used as a substrate and thecomposition 1 shown in Table 1 was coated on the hydrophobic film ofthis substrate. An colored oil (liquid obtained by dissolving 0.1 wt %of Sudan Black B (manufactured by Wako Pure Chemical Industries, Ltd.)in octane) was injected to each compartment (cell) surrounded by thethus formed partition wall, and the resulting partition wall-equippedsubstrate was placed in water. Then, a glass plate 2 having a 100nm-thick ITO layer on one side (“20Ω”, manufactured by Nippon SheetGlass Co., Ltd.) was arranged such that the ITO layer of the glass plate2 is provided on the side of the partition wall-equipped substrate andin contact with the partition wall. Thereafter, by sealing the contactportion between the partition wall and the ITO layer of the glass plate2 with a photo-curable epoxy adhesive, a display element having not lessthan 100 cells in the center of the substrate was prepared.

Examples 2 to 13 and Comparative Example 1

A partition wall and a display element were each prepared in the samemanner as in Example 1, except that the respective composition shown inTable 3 or 4 was used and the UV irradiation was performed at therespective exposure dose shown in Table 3 or 4.

5. Evaluations

The partition walls and display elements obtained in Examples andComparative Example were evaluated by the following methods. The resultsthereof are shown in Table 3 or 4.

5-1. Shape

For each of the partition walls obtained in the above-described Examplesand Comparative Example, the cross-sectional shape was observed under anelectron microscope, and the height of the partition wall (lengthcorresponding to the vertical direction in FIG. 1), the width of thepartition wall in contact with the ITO layer (base width) and the widthof the partition wall on the side opposite to the side in contact withthe ITO layer (top width) were measured under an SEM (model “S-4200”,manufactured by Hitachi High-Technologies Corporation).

It is noted here that the height of each partition wall was measured at5 arbitrary points and an average thereof is shown in Table 3 or 4.Further, using the standard deviation, 6, of the measurements taken atthe 5 points, the in-plane uniformity of the height of the partitionwall was evaluated using the following equation:Height in-plane uniformity(3σ)=3×σ5-2. Evaluation of Thermal Linear Expansion Coefficient

For each of the partition walls obtained in the above-described Examplesand Comparative Example, a film piece of 20 μm in thickness, 10 mm inlength and 10 mm in width was fixed upright in a TMA (thermal MechanicalAnalysis) SS6100 apparatus (manufactured by Seiko Instruments Inc.), anda load of 1 g was applied thereto using a probe. In order to eliminatethe thermal history of the film, after once heating the film from roomtemperature to 200° C. at a rate of 5° C./min, the film was cooled andagain heated from room temperature at a rate of 5° C./rain. Then, agraph showing the relationship between the thus obtained results and thetemperature was prepared. The thermal linear expansion coefficient wasdetermined from the slope of the thus obtained graph between 50° C. and150° C.

5-3. Evaluation of Difference in Thermal Linear Expansion Coefficient

The difference in thermal linear expansion coefficient was evaluatedusing the following equation.Difference in thermal linear expansion coefficient=(Thermal linearexpansion coefficient of each partition wall obtained in Examples andComparative Example)−(Thermal linear expansion coefficient of surfacelayer)

It is noted here that the thermal linear expansion coefficient of theabove-described 450 μm-thick hydrophobic film (amorphousfluorine-containing polymer “AF1600”, manufactured by DuPont Co.) wasmeasured in the same manner as in the above “5-2. Evaluation of ThermalLinear Expansion Coefficient”, except that a film made of the polymer“AF1600” having a thickness of 20 μm, a length of 10 mm and a width of10 mm was used. This film had a thermal linear expansion coefficient of100 ppm/K.

Further, the thermal linear expansion coefficient of the above-described100 nm-thick ITO layer was determined using an ITO layer-equipped glasssubstrate (“20Ω”, manufactured by Nippon Sheet Glass Co., Ltd.). Thethermal linear expansion coefficient of the ITO layer was calculated asa difference between the thermal linear expansion coefficient of the ITOlayer-equipped glass substrate (“20Ω”) and that of the glass plate ofthe “20Ω” from which the ITO layer was detached, which values weremeasured in the same manner as in the above “5-2. Evaluation of ThermalLinear Expansion Coefficient”. The thermal linear expansion coefficientof the ITO layer was found to be 10 ppm/K.

5-4. Outer Appearance

Using a heat cycler (TSA-40L, manufactured by Tabai Espec Co., Ltd.),each of the display elements obtained in Examples and ComparativeExample was cooled to −40° C. at a cooling rate of 2° C./min andretained at −40° C. for 10 minutes, followed by heating to 100° C. at aheating rate of 2° C./min and subsequent retention at 100° C. for 10minutes. Taking this process as 1 cycle, the cycle was repeated 100times. Then, the partition wall and the part of the surface layer incontact therewith (hydrophobic film or ITO layer) were observed under amicroscope. A case where cracking or detachment occurred between thepartition wall and the surface layer was evaluated as “presence ofcracking”, whereas a case where neither cracking nor detachment occurredwas evaluated as “no cracking”.

5-5. Evaluation of Operational State of Display Element

For each of the display elements obtained in Examples and ComparativeExample, a direct-current voltage of 10 V/10 μm intervals was appliedbetween the pair of ITO layers sandwiching the partition wall, coloredoil and water. In 100 cells that were formed on the substrate center ofeach display element obtained in Examples, the application of thevoltage caused contraction of the colored oil (change into ahemispherical shape), making the backside transparent and, when theapplication of the voltage was terminated, color display was restored inall of the cells.

Taking application of the above-described direct-current voltage andtermination of the application as 1 cycle, the cycle was repeated 100times. Thereafter, in a condition where the application of the voltagewas terminated, a case where defective color display did not occur inmore than 80% of the cells was judged as “good” operational state of thedisplay element; a case where defective color display occurred in notless than 20% to less than half of the cells was judged as “rather good”operational state of the display element; and a case where defectivecolor display occurred in not less than half of the cells was judged as“poor” operational state of the display element.

TABLE 3 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Photosensitive composition for formation Composi- Composi-Composi- Composi- Composi- Composi- Composition 7 of partition wall tion1 tion 2 tion 3 tion 4 tion 5 tion 6 Exposure dose of prebaked coatingfilm 330 350 350 300 300 250 250 (mJ/cm² @ 365 nm) Shape of partitionwall Height (μm) 20 20 20 20 20 20 20 Height in-plane 0.25 0.21 0.160.16 0.16 0.16 0.16 uniformity (3σ) Top width (μm) 8 9 8 10 8 9 9 Basewidth (μm) 9 10 11 10 9 9 9 Partition Thermal linear expansion 140 120100 80 60 40 20 wall coefficient of partition wall property (ppm/K)Display Difference Hydrophobic layer 40 20 0 −20 −40 −60 −80 element inthermal ITO layer 130 110 90 70 50 30 10 linear expansion coefficientOuter appearance no cracking no cracking no cracking no cracking nocracking no cracking no cracking Element Operational Reliability rathergood rather good good good good good good property state

TABLE 4 Comparative Example 8 Example 9 Example 10 Example 11 Example 12Example 13 Example 1 Photosensitive composition for Composition 8Composition 9 Composition Composition Composition CompositionComposition formation of partition wall 10 11 12 13 14 Exposure dose ofprebaked coating film 300 300 300 300 300 300 360 (mJ/cm² @ 365 nm)Shape of partition wall Height (μm) 20 20 20 20 20 20 20 Height 0.160.21 0.16 0.16 0.25 0.25 0.86 in-plane uniformity (3σ) Top width 10 1010 9 9 10 7 (μm) Base width 10 10 11 9 10 10 9 (μm) Partition Thermallinear expansion 40 40 40 60 60 60 180 wall coefficient of partitionproperty wall (ppm/K) Display Difference Hydrophobic −60 −60 −60 −40 −40−40 80 element in thermal layer linear ITO layer 30 30 30 50 50 50 170expansion coefficient Outer appearance no cracking no cracking nocracking no cracking no cracking no cracking presence of crackingElement Operational Reliability good good good good good good poorproperty state

6. Evaluation Results

It was confirmed that, in the display elements obtained in Examples 1 to13, defective color display did not occur in not less than half of thecells even after the above-described cycle was repeated 100 times.Particularly, in the display elements obtained in Examples 3 to 13, evenafter the cycle was repeated 100 times, defective color display did notoccur in more than 80% of the cells. In other words, it was found thatthe display elements obtained in Examples are capable of smoothly andstably changing the state of the colored oil (non-polar liquid) for aprolonged period of time.

Furthermore, the use of such a composition allowing the resultingpartition wall to have a thermal linear expansion coefficient in theabove-described range enabled to easily obtain, for example, a partitionwall having excellent height in-plane uniformity; therefore, it wasfound that a partition wall of a desired shape can be thereby easilyformed.

Meanwhile, in the evaluation of the operational state of the displayelement obtained in Comparative Example 1, abnormality was observed inthe change (contraction behavior) of the colored oil into asubstantially hemispherical shape when the application of voltage wasterminated, and defective color display occurred in not less than halfof the cells; therefore, poor evaluation was given.

DESCRIPTION OF SYMBOLS

-   -   10: Display element    -   11: First electrode layer stack    -   12: Second electrode layer stack    -   13: Partition wall    -   14: Non-polar liquid    -   15: Polar liquid    -   16: Housing space (pixel region (cell))    -   20: Partition wall formed on ITO layer    -   21: Partition wall    -   22: ITO layer    -   23: Cell

The invention claimed is:
 1. A display element, comprising: a firstelectrode layer stack; a second electrode layer stack, the firstelectrode layer stack and the second electrode layer stack facing eachother to form a housing space therebetween; a partition wallcompartmentalizing said housing space; a polar liquid and a non-polarliquid each disposed in the housing space and being immiscible with eachother; and a surface layer provided on a surface of at least one of thefirst and second electrode layer stacks and being in contact with saidpartition wall and in contact with at least one of the polar liquid andthe non-polar liquid, wherein a material of said partition wall and amaterial of said surface layer are selected such that an absolute valueof a difference in thermal linear expansion coefficient between saidpartition wall and said surface layer is adjusted to 150 ppm/K or less.2. The display element according to claim 1, wherein said partition wallhas a thermal linear expansion coefficient of from 0.1 to 150 ppm/K. 3.The display element according to claim 1, wherein said partition wall isa film obtained from a photosensitive composition.
 4. The displayelement according to claim 1, wherein said partition wall is a filmobtained from a negative photosensitive composition.
 5. The displayelement according to claim 4, wherein said negative photosensitivecomposition comprises an alkali-soluble polymer, a cross-linking agentand a photoinitiator.
 6. The display element according to claim 5,wherein said cross-linking agent is at least one compound selected fromthe group consisting of an ethylenically unsaturated group-containingcompound, an epoxy group or oxetanyl group-containing compound and analkoxyalkyl group-containing compound.
 7. The display element accordingto claim 5, wherein said alkali-soluble polymer comprises at least onefunctional group selected from the group consisting of a carboxyl group,a phenolic hydroxyl group and a silanol group.
 8. The display elementaccording to claim 5, wherein said alkali-soluble polymer is at leastone polymer selected from the group consisting of an acrylic resin, apolyimide, a polybenzoxazole, a polysiloxane, a polyolefin, a cardoskeleton-containing resin and a novolac resin.
 9. The display elementaccording to claim 5, wherein said alkali-soluble polymer has aweight-average molecular weight of from 1,000 to 100,000.
 10. Anelectrowetting display, comprising the display element according toclaim
 1. 11. The electrowetting display according to claim 10, furthercomprising a color filter layer.
 12. The display element according toclaim 1, wherein the partition wall has the thermal linear expansioncoefficient of from 0.1 to 100 ppm/K.
 13. The display element accordingto claim 12, wherein the material of said partition wall and thematerial of said surface layer are selected such that the absolute valueof the-difference in thermal linear expansion coefficient between saidpartition wall and said surface layer is adjusted to 100 ppm/K or less.14. The display element according to claim 12, wherein the partitionwall comprises at least one polymer selected from the group consistingof an acrylic resin, a polyimide, a polybenzoxazole, a polysiloxane, apolyolefin, a cardo skeleton-containing resin and a novolac resin, andthe surface layer comprises a fluorine-containing material.
 15. Thedisplay element according to claim 14, wherein the material of saidpartition wall and the material of said surface layer are selected suchthat the absolute value of the difference in thermal linear expansioncoefficient between said partition wall and said surface layer isadjusted to 100 ppm/K or less.
 16. The display element according toclaim 12, wherein the partition wall comprises at least one polymerselected from the group consisting of a cross-linked acrylic resin, across-linked polyimide, a cross-linked polybenzoxazole, a cross-linkedpolysiloxane, a cross-linked polyolefin, a cross-linked cardoskeleton-containing resin and a cross-linked novolac resin, and thesurface layer comprises a fluorine-containing material.
 17. The displayelement according to claim 16, wherein the material of said partitionwall and the material of said surface layer are selected such that theabsolute value of the-difference in thermal linear expansion coefficientbetween said partition wall and said surface layer is adjusted to 100ppm/K or less.
 18. A photosensitive composition for forming a partitionwall of a display element, the display element comprising a firstelectrode layer stack and a second electrode layer stack which face eachother to form a housing space therebetween, said partition wallcompartmentalizing the housing space, a polar liquid and a non-polarliquid each disposed in the housing space and being immiscible with eachother, and a surface layer provided on a surface of at least one of thefirst and second electrode layer stacks and being in contact with saidpartition wall and in contact with at least one of the polar liquid andthe non-polar liquid, wherein components of said photosensitivecomposition and a material of said surface layer are selected such thatan absolute value of a difference in thermal linear expansioncoefficient between said partition wall and said surface layer isadjusted to 150 ppm/K or less.
 19. The photosensitive compositionaccording to claim 18, which is a negative composition comprising analkali-soluble polymer, a cross-linking agent and a photoinitiator.